The present invention relates to a process and an apparatus for exhausting fumes and oxide particles generated by a plasma-arc cutting machine.
Generally a flame cutting machine having many torches is used widely in order to cut steel plate to a desired shape, but recently the plasma-arc cutting machine tends to be used frequently for the sake of cutting speed and quality improvement of the product. In the flame cutting machine, cutting wastes in the forms consisting of comparatively small iron oxide and solidified molten metal are produced, the small oxide particles are in the form of sparks and generate an air contamination by turning said particles into dust and fumes. But especially in the plasma-arc cutting machine, fumes and harmful gases are generated together with a large quantity of dust and smoke, as compared with the flame cutting machine, the working environment is significantly deteriorated by surrounding air contamination, and the health of workers and other nearby persons can be harmed. An arrangement of apparatus for exhausting fumes in the plasma-arc cutting machine is indispensable. An enlargement of accessory facilities together with exhausting and treating apparatus for cutting slag and scrap impedes an improvement of productivity, and reduction of these accessory facilities is becoming a subject of great interest.
Heretofore, in the flame cutting machine and the plasma-arc cutting machine, dividing a fixed board for cutting into small chambers by many partition plates, arranging in succession a main duct in each small chamber through dampers and the like, which are capable of opening and shutting respectively, and opening the dampers in the neighborhood of the cutting torch, has been the method for exhausting fumes locally. In such a method, a long main duct over whole extent of the fixed board for cutting, and numerous dampers which are arranging in succession between the main duct and small chambers and the control mechanism for opening and shutting are required. The cost for accessory facilities involves massive expenditures, therefore there are defects which render difficult putting said method to practical use.
Also, U.S. Pat. Nos. 3,486,744 and 3,743,259 and the like are proposed as means for reducing air contamination which is produced from the flame cutting machine by use of a fluid.
In the former, a stream of water is supplied continuously to an inclined conduit which is arranged under the cutting torch, the oxide waste particles and the like which are generated in the cutting operation are entrained by this stream of water, and they are carried off to the precipitating pit. Since a considerable distance exists between the material being cut and a stream of pure water, the fumes of excess quantities and oxide particles run off and contaminate the atmosphere, and consequently an effect for exhausting fumes is not provided. The latter patent is an improvement of the former, and is so arranged that a spray-treating means for washing much more efficiently the environmental atmosphere of the cutting apparatus is equipped directly below the supporting table (fixed board for cutting) supporting the material which is cut. Air which is in existence downstream from the material being cut is saturated sufficiently and fumes and oxide which are generated during the cutting operation are filtered from the atmosphere.
Further, U.S. Pat. No. 3,851,864 is disclosed as the means which controls noises and fumes generated by the plasma-arc cutting but in this patent the material which is cut and an end of the torch nozzle are immersed in water, or a stream of water is supplied to a nozzle end and portions which is cut, and the cutting operation is carried out in the water. Consequently, the fumes are confined in the water and air contamination is reduced, but new problems for arrangement of drainage treating apparatus caused by water contamination arise. Also, there are defects which affect the quality aspect, including a deterioration of the roughness of the cutting surface and the accuracy of the cutting dimension and the like, as compared with the usual plasma-arc cutting (in the atmosphere).
At all events, in the above mentioned means for decreasing and controlling the atmospheric contamination which results from plasma-arc cutting by the use of a fluid, generally water, a large-scale foundation work consisting of inclined conduit, precipitating pit, large capacity water tank and the like and a water circulating apparatus by a pump are required for the circulating equipment for the water supply in the lower part of the fixed board for cutting (supporting table). Therefore that means requires a massive expenditure.